Help Interpreting SleepyHead Data

[richart]

I have been reading about the SleepyHead data, but frankly I am more confused than ever. The program presents a huge amount of data. Can someone help me with this sample of charts and tell me what is going on? I can't seem to get my AHI down to 5 or below.

[robysue]

I have been reading about the SleepyHead data, but frankly I am more confused than ever. The program presents a huge amount of data. Can someone help me with this sample of charts and tell me what is going on? I can't seem to get my AHI down to 5 or below.

You might want to go through the Pugsy's Pointers thread that's at the top of the Stickies to learn all about the data presented in SH.

In looking at the data you do present, there's an obvious concern: The large number of CAs being recorded each night. Your CAI is by far the largest piece of the overall AHI on most of these nights the CAI > 5.0 all by itself. It's also significant that your CAI increased after you increased the pressure from 12cm to 13cm. These two things are enough to warrant caution in assuming that you need additional pressure to bring your AHI down below 5.0. CAs occur when the airway is already clear (not blocked) and additional pressure does not prevent them. Moreover, about 10-15% of new PAPers develop problems with pressure-induced central apneas, which means that the CPAP pressure itself can cause CAs to occur. In this case, more pressure often causes more CAs to occur.

Now the thing is, it can be tough to figure out whether the CAs in data like yours are real CAs that would be scored on an in-lab sleep test or whether they're wakeful breathing that is being mis-scored as CAs, which would not be scored on an in-labe sleep test because they actually occurred when you were awake.

On two of the nights at 13cm, there are a lot of breaks in the Flow Rate curve that appear to indicate you woke up and turned the machine off and back on. How sound do you think you were sleeping between those wakes? And how sound do you think you were sleeping on the night of March 12 (the night with the highest CAI and highest AHI)?

Here's what I would do if this data were my data:

1) I'd lower the pressure back down to 12 cm to see whether the number of CAs decreases.

2) I'd recheck the diagnostic and titration sleep study reports to see whether CAs were mentioned on either of them. If I didn't have copies of the sleep study reports, I would start the process of getting them for my records.

3) If I was pretty sure I was asleep during most of the times the CAs are being scored, I'd let my sleep doc know that my AHI is consistently running above 5.0 and that CAs make up a large chunk of the events. If the doc suggeseted or authorized that pressure increase from 12 to 13cm, I'd be sure to tell him that the number of CAs has grown with the pressure increase and that at 13cm the CAI is often above 5.0 all by itself.

4) If CAs ARE mentioned on the sleep study reports, I would insist on having a follow-up in-person meeting with the sleep doc (not a PA or nurse practitioner) to ask specifically what his/her opinion is concerning the CAs being recorded by the machine: The probability that the CAs in your nightly data are real goes up if CAs are reported as a problem on either of the sleep study reports.

I don't want to sound too alarming about the CAs: While 10-15% of new PAPers develop some problems with pressure-induced CAs, the CAs in many of those PAPers will go away with time. In other words, your sleep doc may recommend watchful waiting as a first response to seeing this kind of data. If the number of CAs starts to drop in 3-4 weeks, then most likely they're a self-limiting problem that won't be a long term issue. If the number of CAs continues to be this large (or continues to increase) after 3-4 weeks AND you're pretty sure you are actually asleep when the CAs are being recorded, then the next step may be a recommendation for a change of machine and a titration for the new machine.

[richart]

Robysue, thanks much for the response. You have certainly narrowed up the focus some for me. On the night of March 12 when I had the large number of CAs, I did not sleep soundly for much of the night, spent a lot of time fiddling with the mask, and turned the machine off a couple of times when I got up to take a break. I had changed the pressure on my own from 12 to 13 in an attempt to bring down the overall AHI which sounds like it may have been the wrong move based on your observations.

Help me a bit with this statement, "CAs occur when the airway is already clear (not blocked) and additional pressure does not prevent them. Moreover, about 10-15% of new PAPers develop problems with pressure-induced central apneas, which means that the CPAP pressure itself can cause CAs to occur. In this case, more pressure often causes more CAs to occur." Does 'CA' indicate 'Central Apnea' or 'Clear Airway Apnea', or are they one and the same??? I will pull out my original sleep study tonight and see if there is any mention of them.

The SleepyHead program presents a huge amount of data and after reading Pugsy's Pointers and other resources I was a bit overwhelmed. Thanks for the pointers and an area to focus on!

[robysue]

Help me a bit with this statement, "CAs occur when the airway is already clear (not blocked) and additional pressure does not prevent them. Moreover, about 10-15% of new PAPers develop problems with pressure-induced central apneas, which means that the CPAP pressure itself can cause CAs to occur. In this case, more pressure often causes more CAs to occur." Does 'CA' indicate 'Central Apnea' or 'Clear Airway Apnea', or are they one and the same??? I will pull out my original sleep study tonight and see if there is any mention of them.

Unfortunately, CA can (and does) mean both Central Apnea (as scored on an in-lab PSG or a home sleep test that has belts around your chest and abdomen) and Clear Airway Apnea (as scored by a full efficacy data PAP machine.)

Central Apneas and Clear Airway Apneas are not quite the same thing, but the presumption by the folks who designed the current "CA detection algorithms" is that counting Clear Airway Apneas gives a very good approximation for the number of Central Apneas.

To make this a bit clearer:

Central Apnea as scored on a real sleep test
On a real sleep test where there are belts around your chest and abdomen, the belts are used to measure your effort to breathe. When there is no air moving in or out of your lungs for > 10 seconds AND you are making an effort to breath (as measured by the belts), the problem is assumed to be a collapsed upper airway and an OA is scored.

A Central Apnea is scored when there is no air moving into or out of your lungs for > 10 seconds AND the belts show there is no effort being made to breathe. The assumed cause of the apnea is that your brain forgot to send a signal to your lungs and diaphragm to "Inhale Now". The patency of the upper airway is not considered important---it's the fact that your brain forgot to tell your lungs to "Inhale Now" that is the problem.

It turns out that on sleep tests, the tech can also score what is known as a "Mixed Apnea". A Mixed Apnea starts out looking like a Central Apnea, but ends up looking like an Obstructive Apnea. In other words, there's no air moving in or out of your lungs for at least 10 seconds AND at the start of the apnea there is NO effort to breathe (based on the data from the belts) AND at some point you start trying to breathe, but no air is getting into or out of your lungs. The idea is that the start apnea was caused by a Central problem (your brain forgot to send the "Inhale Now" message) AND at the same time or shortly after the apnea started, your upper airway collapses. Hence when the brain realizes it needs to send an "Inhale Now" message, the effort to breathe resumes, but because of the collapsed airway, no air can get in to the lungs.

Clear Airway Apnea as scored by a CPAP/APAP
Several manufacturers of CPAP/APAPs have designed algorithms designed to test the patency of the upper airway when an apnea is occurring. The Resmeds use a "FOT" algorithm that involves rapidly oscillating the pressure being delivered; the PR machines use a "PP" algorithm that sends periodic "pressue pulses" down the airway. The machine uses the backpressure in the hose to determine whether the airway is most likely clear (unobstructed) or most likely obstructed (blocked). If the airway appears to be blocked, the machine scores an OA. If the airway appears to be clear, the machine scores a CA.

Now here's why machine scored Clear Airway Apneas (machine CAs) are usually thought of as good approximations for detecting real Central Apneas (sleep test CAs): If the machine detects no air is moving into or out of your lungs for > 10 seconds and the airway is not blocked, then it's reasonable to assume the airway has not collapsed and thus the problem is most likely caused by a lack of effort to breath---i.e. there's a high probability that you are experiencing a real central apnea. If the machine detects a blocked airway, the machine assumes that an effort to breath is happening but no air can get through the blocked airway, and thus an OA is scored.

There is always a chance that a real Central Apnea or Mixed Apnea might be mis-scored by a CPAP/APAP as an OA since the airway can be blocked in a Central Apnea and is blocked in a Mixed Ppnea. There is almost no chance that a real OA will be mis-scored as a Clear Airway CA since the airway will be blocked in a real OA.

[QueSera]

I haven't asked my question yet, but robysue, you sure answered it here. My OA result is pretty good most nights, but my CA score keeps my AHI crazy high. I was just about to lower my pressure a bit for tonight, and now I definitely will. Im going to print out your reply above and use it as my guide. Thank you.

[richart]

Robysue, thanks for the very clear and concise explanation. I went back and checked my last sleep study done in 2011 and it showed 1 central apnea, 20 obstructive apneas and 50 hypopneas for an AHI of 30.3. Last night was the best night I have had since I have been back on CPAP for 5 weeks. My AHI was 2.21 and the CAs were greatly reduced. I noticed that I spent very little time messing with the mask and seemed to have a good seal for most of the night. Hopefully as I grow more accustomed to the CPAP therapy and have good luck with my mask, I will also have better numbers. Again, thanks for taking your time to help me understand a little better what SleepyHead is trying to tell me!